The autoclaving process is generally defined as a high-temperature damp-heat (steam) process for completely destroying all viable microorganisms including organisms such as viruses and spores. Considering the possible infection risk associated with improper sterilization (i.e. failing to reach the sterilization condition), monitoring the sterilization process is always beneficial. Standard practice involves sterilizing the articles to be sterilized in the presence of an indicator, and then evaluating the sterilization process based on the change occurred to the indicator (affected by one or more sterilization condition(s)). Currently there are two general types of autoclave indicators, i.e. biological indicators and chemical indicators. Because a relatively longer period is needed to read the result of biological indicators after sterilization, chemical indicators, which can be read at the end of the sterilization process right away, have become very popular for the normal operation in hospitals, clinics and the like.
In some existing chemical indicating systems, an indicating composition using a nitrocellulose resin system as described in U.S. Pat. No. 288,979 and GB872136 is employed. Such an indicating composition is based on an organic thermochromic dye, or a derivative thereof, or a metallic salt compound, and can be coated on a paper substrate so as to make an autoclave tape.
Most of the existing indicators are based on the use of organic solvents such as ketones, hydrocarbons, alcohols, or esters, which can harm the environment and cause safety issues associated with manufacturing and handling.